On the effects of circulation, sediment resuspension and biological incorporation by diatoms in an ocean model of aluminium

Abstract. The distribution of dissolved aluminium in theWest Atlantic Ocean shows a mirror image with that of dissolvedsilicic acid, hinting at intricate interactions betweenthe ocean cycling of Al and Si. The marine biogeochemistryof Al is of interest because of its potential impact ondiatom opal remineralisation, hence Si availability. Furthermore,the dissolved Al concentration at the surface oceanhas been used as a tracer for dust input, dust being the mostimportant source of the bio-essential trace element iron tothe ocean. Previously, the dissolved concentration of Al wassimulated reasonably well with only a dust source, and scavengingby adsorption on settling biogenic debris as the onlyremoval process. Here we explore the impacts of (i) a sedimentsource of Al in the Northern Hemisphere (especiallynorth of ?40? N), (ii) the imposed velocity field, and (iii)biological incorporation of Al on the modelled Al distributionin the ocean. The sediment source clearly improves themodel results, and using a different velocity field shows theimportance of advection on the simulated Al distribution. Biologicalincorporation appears to be a potentially importantremoval process. However, conclusive independent data toconstrain the Al / Si incorporation ratio by growing diatomsare missing. Therefore, this study does not provide a definitiveanswer to the question of the relative importance of Alremoval by incorporation compared to removal by adsorptivescavenging